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Current most accepted idea is that a stony asteroid disintigrated in the atmosphere. It came in on a fairly oblique approach and blew up about 5 miles up with about 15 megatons of power.

Thing is, since no one investigated until decades after the impact, they cant really tell what is blast effect or what is natural effect when it comes down to the small details that would give a definitive answer.

Actually I heard recently that they changed it from an asteroid to a comet. They found some evidence for it but I forgot about where I found this out.

Strangely enough one Russian scientist has a theory that an alien spacecraft flew into the comet in mid air to protect the Earth. He later explained that he was looking for some substance that could only be created in space. Not sure what he was looking for though.

Strangely enough one Russian scientist has a theory that an alien spacecraft flew into the comet in mid air to protect the Earth. He later explained that he was looking for some substance that could only be created in space. Not sure what he was looking for though.

Yes, I read that as well recently possibly in an article in SpaceFlightNow (?). It was within the last month or so, I think.

Alan

Originally Posted by GalacticBeatDown

Actually I heard recently that they changed it from an asteroid to a comet. They found some evidence for it but I forgot about where I found this out.

Strangely enough one Russian scientist has a theory that an alien spacecraft flew into the comet in mid air to protect the Earth. He later explained that he was looking for some substance that could only be created in space. Not sure what he was looking for though.

Tunguska

Current most accepted idea is that a stony asteroid disintigrated in the atmosphere. It came in on a fairly oblique approach and blew up about 5 miles up with about 15 megatons of power.

Thing is, since no one investigated until decades after the impact, they cant really tell what is blast effect or what is natural effect when it comes down to the small details that would give a definitive answer.

Hi korjik, the place where the impact occured has been found. It is very remote and
difficult to access. A crater was found, but made by an asteroid or comet, not determined.
Matters not. What really matters is that it will happen again, and how can we
circumvent it. I'm afraid the saying ' tomorrow is dead through lack of interest' applies.
We have dedicated amateurs who devote much of their time in tracking rogue
asteroids, but there is no world consensus on how to mitigate the effects of another
strike, or even how to anticipate and avoid it.
Much like in the event of a massive solar flare. Our power sources would be fried.
We have a current response time of 20 minutes, to shut down relays and converters
to minimise the damage. Somewhat a bit late, the solar flare would reach us in 8 mins.
And we worry about global warming.
The same with Yellowstone, sitting on a massive magma deposit that will erupt once
the pressure reaches critical.......
Nokton.

Yellowstone

Originally Posted by mugaliens

"...once the pressure reaches critical... Nokton?"

What's a critical Nokton?

Just kidding, nokton...

Hi mugaliens, pleased your interest. Yellowstone sits on a vast magma field.
' Old Faithful ' demonstrates the power beneath, and the pressure is building.
By critical I mean when the internal pressure overcomes the strata above it
and explodes as a super massive volcano......Check it out my friend.
As for global warming, in 986 AD, Eric the Red colonised Greenland,
so called because it was a green and pleasant land, it was.
Point is, the polar bears survived there at that time. Now we are told,
while most of Greenland is still iced up, the polar bears are at risk,
God give me a prayer, let reason and logic intrude my dreams and reverie.
Nokton

Exactly. I for one am tired of billions of dollars thrown at chicken little research.

Tunguska was an amazing event, and I'm glad it didn't occur near a populated area! I'm willing to bet that such an event is likely to occur once in every person's lifetime.

Hi mugaliens, am with you at throwing money at research where the parameters are not
set.
If I may, the huge magma chamber beneath Yellowstone is a fact.
should it fracture, half the northern US would be decimated, it will.
Tunguska should have been a wake up call. But with the cold war and all, who
would listen?
Global warming is not the real issue here, you are right in predicting another hit
in our lifetime. And we so ill prepared for it.
Nokton

Let's try to stay on topic here, please. This may seem heavy-handed, but the whole point of this section of the forum is to provide straightforward, mainstream answers to space and astronomy questions, and the less noise thrown in, the better. Ideally, someone months from now can do a search on the original question, find this thread, and look through it to find the answer without having to read through a bunch of marginally relevant posts. Thanks.

Hi mugaliens, am with you at throwing money at research where the parameters are not
set.
If I may, the huge magma chamber beneath Yellowstone is a fact.
should it fracture, half the northern US would be decimated, it will.

Since "half the world's geothermal features are in Yellowstone, fueld by the ongoing volcanism of the Yellowstone Caldera, perhaps tapping into it to supply the US energy needs would take some of the pressure off...

Tunguska should have been a wake up call.

...

Global warming is not the real issue here, you are right in predicting another hit
in our lifetime. And we so ill prepared for it.
Nokton

Agreed. We could not have done anything about Tunguska. My concern is that we may still not be able to do anything about it, as it was quite small. NASA's congressional mandate is to catalogue all neath-Earth objects (NEOs) that are at least 1 km wide.

Tunguska, by comparison, was just "a few tens of meters across," which would put it between 3,000 and 37,000 times less massive than the minimum size required of NASA's search.

And NASA's search is by no means complete, with approximately 16% of the ones 1 km acoss and large having yet to be detected.

Which means, of course, that potential Tunguska-like objects may yet be both pentiful and undetected.

what really happened in tunguska, russia? was it a comet or an asteroid, some even said it's a massive earthquake. have astronomers agreed on what happened there or they still don't know up until now?

As far as I know, scientists still are not sure what happened at Tunguska. They are pretty certain it was an extraterrestrial impactor but the debate centers around the composition of the object. Some say comet, some say meteoroid. Some of the key reasons for dispute are due to the presumed low angle of entry and the lack of obvious impact crater. It is presumed a comet may not withstand a low angle entry without disentegrating, while an iron or rocky core may survive low angle entry. Recently, it is believed, the Tunguska crater has been found under Lake Cheko, however dispute still exists. If Lake Cheko is the impact crater, it is elliptical, which is unusual except, possibly in very low angle entries, under the right conditions. Most impact craters are circular even though the impactor rarely strikes perpenticular to the surface.

ToSeek, and the path of this site

Originally Posted by ToSeek

Let's try to stay on topic here, please. This may seem heavy-handed, but the whole point of this section of the forum is to provide straightforward, mainstream answers to space and astronomy questions, and the less noise thrown in, the better. Ideally, someone months from now can do a search on the original question, find this thread, and look through it to find the answer without having to read through a bunch of marginally relevant posts. Thanks.

Take your point, and concur, apologise for the deviation my posts caused. If I may,
ToSeek, was looking at the broader picture Tunguska painted. The threat to life as
we know it, by astronomical events such as a rogue asteroid impact, which I feel
falls into a space astronomy scenario, and also local events that may impact on
our survival as a species to understand space and astronomy.
My response to your post, ToSeek, is not condescending, but rather an explanation
of my concern for the future of Mankind.
With sincere respect,
Nokton.

The OP asked a good question and as may be the case information recently spoken of. Not that there was any new information its just the compiling of what information we have. No impact creator. No debris found. A large area of radially flattened forest. Broken by what must have been a significant explosive event. Fortunately this very sparsely populated area served us well in respect that it lay undisturbed for years and not a single death was recorded. The same facts also served as a disadvantage also, and for the same reasons. Between 5 and 30 megatons is a wide range... A very strong energy transfer. Heat, shock wave, noise. wind. Dust., and still more heat.
What really happened ? An object came into Earth's atmosphere at high velocity and a shallow angle and because of the energy transfer mechanics did not have the integrity to reach ground zero. It exploded while still high in our atmosphere. The shock wave of that explosion did all the damage and little if any of the actual object has ever been found. Suggesting it was largely ice is a logical conclusion. A comet.

Last edited by astromark; 2009-Jul-13 at 09:59 AM.
Reason: added word for clarity.

There seems to be an overwhelming concensus, at least on this board, that the object in question was a comet, but that is not confirmed. There is an anomolous chunk of something sitting in the sediments of the Cheka lake bottom. There is research to show Lake Cheka could be no more than 100 years old based on recent sediment measurements. There is reasonable doubt that a comet can survive a low entry angle and still produce a crater. So, if Lake Cheka does indeed prove to be an impact crater, it is possible the object was something other than a comet or it was the hypothetical rocky core of a comet.

Here is a very interesting website which allows one to try different impact scenarios and then examine the theoretical effects. This is cool

As far as I know, scientists still are not sure what happened at Tunguska. They are pretty certain it was an extraterrestrial impactor but the debate centers around the composition of the object. Some say comet, some say meteoroid. Some of the key reasons for dispute are due to the presumed low angle of entry and the lack of obvious impact crater. It is presumed a comet may not withstand a low angle entry without disentegrating, while an iron or rocky core may survive low angle entry. Recently, it is believed, the Tunguska crater has been found under Lake Cheko, however dispute still exists. If Lake Cheko is the impact crater, it is elliptical, which is unusual except, possibly in very low angle entries, under the right conditions. Most impact craters are circular even though the impactor rarely strikes perpenticular to the surface.

I find it interesting that only small fragments of the meteor that created Barringer's Crater in NM actually exist. It appears most were either melted or vaporized.

It's been shown that an impact crater remains relatively round despite the impact angle. That holds, though, only to the point where the meteor no longer burrows, but instead skips. A heavy glancing blow caused by a very shallow impact angle would indeed create an oval depression, while simultaneously resulting in the near total disintegration of the meteor. What little did remain would travel for miles, if not hundreds or even thousands of miles, downrange.

The area itself is a peat bog, which raises the question of how much damage a glancing blow, like a rock skipping off the water, would actually do to the terrain. While a few experiments were done in the mid-1960s which indicated the approach angle was about 30 deg, particularly given the butterfly pattern of tree-felling, the approach angle could have been more shallow with the explosion from the impact vaporization of peat bog and meteorite causing the event.

Basically, what I'm getting at is that I think that the available data appear (suspiciously?) consistent with this being a debris object from comet 2P/Encke. Such debris makes up the taurid and beta taurid meteor showers.

Not only is the date of the event on the peak of the beta taurids, but time of day, observed direction of travel, blast pattern etc. appear consistent with atmospheric entry of an object that has an orbit similar to that of comet Encke, as you would expect a taurid to have. If the object that exploded over Tunguska actually did have a former connection with Encke, it would have entered on a roughly West-by-North-West azimuth at a velocity of around 34 km/s, an entry angle of around -45 deg at a local time of 07:15.

My "beef", if you want to call it that, is that people who tried to simulate the disintegration of an object tend to make a very clear distinction between comets and asteroids.

I hold that such a distinction is artificial and may well not be applicable in the case of a comet fragment that was set loose when the cometary nucleus broke into pieces.

Previous simulations appear to have shown that a comet would have disintegrated much higher up, not at the 8 km altitude that appear consistent with the damage pattern, as comets are thought to be composed of fluffy, low-density material.

My reply to that is that:

a.) nobody knows for sure what interior composition comet nuclei have. Data is scarce and stems mostly from few high speed flybys, and we don't whether it is valid to assume that what was observed for one comet also applies to others.

b.) one cannot exclude that even if comet nuclei are *on average* fragile and of low density, they cannot also contain blocks of silicate or carbonaceous rock a few tens of meters across. There is no reason to assume that nuclei should be homogeneous.

Therefore, I put forward the suggestion that one should consider the possibility that:

I.) we have here the case of a chunk of comet Encke that was released in a former fragmentation event and since has been orbiting the sun among other debris set loose in the same event, its orbit and location slowly drifting away from that of comet Encke due to perturbations

II.) Said rock has been undergoing thermal "weathering" following release, losing some of the volatile material that may have been initially attached to it

III.) When said rock entered the Earth atmosphere on June 30, 1908 at 7:15 Tunguska time at the velocity and angle stated above, the remaining volatile material (mainly ice) ablated under the onslaught of atmospheric friction - thereby depositing significant amounts of water in the high atmosphere - and the rock itself survived until an altitude of 8 km, where it disintegrated, creating the blast and damage pattern observed around the epicentre. Perhaps part of it went on and created lake Cheko.

I don't think any of that is very exotic or far fetched. My main point is that we should not push the well-worn distinction between asteroids and comets too far. There certainly is a distinction, but it may be quite "fuzzy and overlapping at the edges"

Oh, and one more thing: If this theory (which by the way is not mine, all I did was to do some added calculations that show that the conjecture is consistent with the observations) holds water, there is no reason to assume that this was the only such large chunk contained in cometary debris.

and the rock itself survived until an altitude of 8 km, where it disintegrated, creating the blast and damage pattern observed around the epicentre. Perhaps part of it went on and created lake Cheko.

I still have seen nor heard no convincing reason for either a cometary or asteroidal fragment to explode. Heat is not likely to be conducted rapidly enough for the external ablative process to allow enough heat into the interior to cause an explosion. Have we seen evidence of frozen blocks of methane or some more volitile hydrocarbons in comets or asteroids that could explode when exposed to heat and Earth's atmospheric oxygen after vaporizing into an explosive cloud?

The blast effect at Tunguska looks very similar to that caused by the side explosion of Mt St Helens. Its hard to believe that that such an explosion could be caused by the breaking up of an object passing through our atmosphere. Either superheated steam, methane or some other explosive mechanism, triggered by heat, must have caused the explosion and blast effect.